In the manufacture of integrated circuits it is desirable to reduce the number of manufacturing steps. In particular, it is desirable to reduce the number of mask and etch steps that are used in the manufacture of complementary bipolar complementary metal oxide semiconductor (CBiCMOS) transistors. The number of mask and etch steps required for to manufacture a transistor is referred to as the “mask count.” Any method for reducing the mask count for a CBiCMOS process flow can reduce manufacturing cost and cycle time. Reducing the mast count, however, requires certain tradeoffs.
One method of reducing the mask count is to combine the extrinsic base implants of the transistor with the source/drain implants of the transistor during the manufacturing process. Because the extrinsic base implants and the source/drain implants are both high dose implants, they can usually share the same implant dose during the manufacturing process. The tradeoff involved in this method is that combining these two implants could result in some counter-doping of the emitter of the transistor if the extrinsic base is self-aligned to the emitter.
Counter-doping can cause an increased resistance in the emitter. An increased resistance in the emitter can adversely affect the direct current (DC) and alternating current (AC) performance of the transistor. Counter-doping can also alter the diffusion in the emitter-base junction. Altering the diffusion in the emitter-base junction of the transistor can also adversely affect the direct current (DC) and alternating current (AC) performance of the transistor.
During the source/drain implant process the emitter can be protected by placing a resist block over it. In order for the emitter to remain self-aligned, however, the resist block must be smaller than the emitter to ensure that the resist block does not extend over the edge of the emitter. An alternative approach is involves counter-doping the emitter with the source/drain implant. This approach has been demonstrated to be feasible but it has certain drawbacks.
Therefore, there is a need in the art for an improved system and method of manufacturing an emitter structure for a transistor. In particular, there is a need in the art for an improved system and method of manufacturing an emitter structure for a complementary bipolar CMOS (CBiCMOS) transistor without increasing the mask count in the manufacturing process.
In an advantageous embodiment of the system and method of the present invention for manufacturing an emitter structure, a protective layer is formed over an emitter layer in a transistor structure and lateral portions of the protective layer and the emitter layer are etched to form an emitter structure. An oxide layer is then deposited over the transistor structure and an etchback process is performed to remove portions of the oxide layer from the top of the protective layer. A source/drain implant process is then performed to implant an extrinsic base region of the transistor. The protective layer protects the emitter structure from the effects of the implant process. Then the protective layer is removed from the emitter structure.
Before undertaking the Detailed Description of the Invention below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like.
Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior uses, as well as to future uses, of such defined words and phrases.